1. Field of the Invention
The present invention generally relates to a call progress tone detection system and, more particularly, to an adaptive call progress tone detection system for enabling communications devices to recognize a variety of different call progress tones.
2. Description of the Prior Art
It is well known that modern communication devices, such as modems, may initiate calls to remote modems by dialing the telephone number of the remote device. The modem, upon dialing, will monitor the telephone line to determine the kind of tones being returned by the PSTN (Public Switched Telephone Network). For example, these tones, which are known as call progress tones, may include a ring back tone, busy tone, dial tone, etc. These various tones are generally audible tones that are used to indicate the state of the call, such as the remote device being busy, the modem placing the line off hook, or the line ringing at the remote device. The tones are generated by an exchange in the PSTN (network) and detected by a subscriber (user). The call initiating device, such as a modem or other communications device, is able to recognize the frequency and cadence (on/off pattern) of the tones and may determine the action it should take based on the particular tone received.
For example, a modem, in initiating a connection to a remote device, will first normally place the telephone line off hook. At that point, the modem is expecting to receive a dial tone. The dial tone, which may be at a certain frequency, once detected by the modem, will then cause the modem to initiate a call to the number of the remote device to be accessed. Upon completion of the dialing of the numbers, the modem waits for a further progress tone to be generated by the network. If the next progress tone is a busy tone, the modem may display a message on the user's computer, notifying the user that the number dialed is busy. However, if the modem receives a ring back tone, it will continue ringing the remote device until an answering tone is received from the remote device or until the modem terminates its dialing procedure.
However, call progress tones and cadences may differ from country to country. Thus, one of the most difficult problems facing the user who requires analog tone recognition is the variability of these tones when calling to or from different parts of the world, thereby necessitating the sale of country specific modems by the manufacturer. Generally, the problem is experienced by the laptop computer-carrying international user, who, for example, may plug his or her machine into a phone jack in another country only to find that the dial tone and cadence resembles that of the user's nation's default busy tone, and thus every attempt is voided by the modems misrecognition of this tone.
Unfortunately, the international traveler may have no other choice than to purchase a country specific communications device, such as a modem, for each country the traveler is visiting. However, such an option is expensive and may cause a great deal of inconvenience to a user who may be forced to remove and install a different modem each time the user enters or leaves a country. Thus, there is no way to manually dial the modem call. A similar problem may apply in a number of other applications as well, such as when sending faxes overseas.
Therefore, what is needed is a system for enabling adaptive call progress tone detection to initiate a learning mode in the call initiating device to enable the device to learn the appropriate tones for the country in question, adapt to the newly learned tones and complete the call to the remote device.